A flat-panel display CRT display typically consists of an electron-emitting device and an oppositely situated light-emitting device. The electron-emitting device, or cathode, contains electron-emissive elements that emit electrons across a relatively wide area. An anode in the light-emitting device attracts the electrons toward light-emissive regions distributed across a corresponding area in the light-emitting device. The anode can be located above or below the light-emissive regions. In either case, the light-emissive regions emit light upon being struck by the electrons to produce an image on the display's viewing surface.
FIG. 1 presents a side cross section of part of a conventional flat-panel CRT display such as that described in U.S. Pat. No. 5,859,502 or 6,049,165. The display of FIG. 1 is formed with electron-emitting device 20 and light-emitting device 22. Electron-emitting device 20 contains backplate 24 and overlying electron-emissive regions 26. Electrons emitted by regions 26 travel toward light-emitting device 22 under control of electron-focusing system 28. Item 30 represents an electron trajectory.
Light-emitting device 22 contains faceplate 32 coupled to backplate 24 of electron-emitting device 20 through an outer wall (not shown) to form a sealed enclosure maintained at a high vacuum. Light-emissive regions 34 overlie faceplate 32 respectively opposite electron-emissive regions 26. When electrons emitted by regions 26 strike light-emissive regions 34, the light emitted by regions 34 produces the display's image on the exterior surface (lower surface in FIG. 1) of light-emitting device 22. Contrast-enhancing black matrix 36 laterally surrounds light-emissive regions 34.
Light-emitting device 22 also contains light-reflective layer 38 situated over light-emissive regions 34 and black matrix 36. Regions 34 emit light in all directions when struck by electrons. Hence, some of the so-emitted light travels backward toward the interior of the display. Layer 38 reflects some of that rear-directed light forward to increase the intensity of the image. In addition, layer 38 functions as the display's anode for attracting electrons toward light-emitting device 22.
The electrons emitted by regions 26 pass through light-reflective layer 38 before striking light-emissive regions 34. In so doing, the electrons lose some energy. The image intensity increase resulting from the light-reflective nature of layer 38 at least partially compensates for any image intensity decrease caused by this electron energy loss. Nonetheless, it would be desirable to further improve the image intensity in a light-emitting device whose anode overlies the device's light-emitting regions.
Each light-emitting region in a light-emitting device such as that of FIG. 1 normally consists of light-emissive particles formed with phosphor material. The constituents of the phosphor particles commonly include elements such as sulfur or/and oxygen. When the light-emissive particles are struck by electrons, some of the sulfur or/and oxygen is commonly released in gaseous form into the interior of the display. The so-released gases can contaminate the display and cause it to degrade.
Petersen et al (“Peterson”), U.S. Pat. No. 5,844,361, addresses the problem of outgassing from phosphor particles in a light-emitting device of a flat-panel CRT display by chemically treating the outer particle surfaces in a way intended to reduce undesired outgassing. FIGS. 2 and 3 depict two examples of Petersen's approach in which light-emissive regions overlie transparent substrate 40. Each light-emissive region consists of a layer of phosphor particles 42.
A coating 44 fully surrounds each phosphor particle 42 in the example of FIG. 2. Coatings 44 can alter the surface chemistry of particles 42 in such a way that they are more thermodynamically resistant to outgassing. Alternatively, coatings 44 can simply be impervious encapsulants that substantially prevent any contaminant gases produced by particles 42 from entering the display's interior. In either case, coatings 44 are provided on particles 42 before they are deposited over substrate 40. The display's anode is formed with aluminum layer 46 provided above composite particles 42/44.
In the example of FIG. 3, coatings 48 of stable oxide are provided on particles 42 after they are deposited on substrate 40. Each coating 48 conformally covers an upper portion of the outer surface of one particle 42. Coatings 48, typically formed by chemical vapor deposition of silane, disiloxane, or tetra-ethyl-orthosilicate, are more thermodynamically resistant to outgassing than are particles 42. Petersen indicates that the display's anode in the example of FIG. 3 can be formed with a conductive layer analogous to aluminum layer 46.
Providing phosphor particles 42 with full coatings 44 before particles 42 are deposited on substrate 40 in the example of FIG. 2 raises concerns that coatings 44 may be damaged during the deposition of particles 42. Also, full coatings 44 may detrimentally affect the formation of the light-emissive regions by absorbing radiation typically utilized in defining the light-emissive regions. Petersen avoids this difficulty with the example of FIG. 3 where partial coatings 48 are deposited on particles 42 after they are deposited on substrate 40. However, Petersen only discloses that coatings 48 may consist of oxide. Petersen does not deal with improving the image intensity.